There’s a new little secret under the hoods of some 2014 Ford Fiesta small cars.

Added as an optional selection for Fiesta buyers during the model year, a new, three-cylinder, gasoline engine with turbocharger is so fuel thrifty, it makes the Fiesta the top gasoline-powered 2014 sedan in fuel mileage in the United States.

In fact, the 2014 Fiesta four door with SE EcoBoost package has government fuel economy ratings as high as those for some diesel-powered sedans from BMW, Audi and Volkswagen. Specifically, the 2014 Fiesta sedan with the three-cylinder, EcoBoost engine is rated at 31 miles per gallon in city driving and 43 mpg on highways for a combined average of 36 mpg.

The numbers aren’t farfetched. The test Fiesta sedan with the little engine averaged 34 mpg even when the driver wasn’t driving to maximize mileage. This translated into a surprising travel range of 421 miles on one tank of gasoline at a cost of $45 at today’s prices for regular unleaded.

The subcompact Fiesta, with attractive styling and a front end that looks like it’s derived from an Aston Martin, is affordable to buy, too.

Starting manufacturer’s suggested retail price, including destination charge, is $17,400 for a front-wheel drive, five-seat, 2014 Fiesta SE sedan with the 123-horsepower, 1-liter, double overhead cam, turbocharged, EcoBoost engine. Only a five-speed manual transmission is offered with this engine, and buyers are limited to getting this engine on only one of the Fiesta’s three trim levels — the mid-level SE.

This means that buyers can’t get a factory-installed rearview camera because that’s only offered on the top Fiesta trim level. They can’t get bigger, flashier wheels, either, on the fuel-sipping Fiesta with EcoBoost engine. But they can add an optional moonroof and heated front seats and still wind up with a retail price, including destination charge, of just over $18,000.

Note that the fuel-savvy Fiesta sedan with the 1-liter powerplant has a starting retail price that’s $2,475 more than the $14,925 starting retail price for a base, 2014 Fiesta sedan. The base 2014 Fiesta sedan comes with 120-horsepower, 1.6-liter, naturally aspirated four cylinder and five-speed, manual transmission that has a government rating of 28/36 mpg. Overall, the base Fiesta sedan has a fuel economy rating that’s 16 percent lower than the smart-mileage Fiesta with the three cylinder.

Competitors include the 2014 Toyota Corolla LE Eco sedan with 140-horsepower, 1.8-liter, naturally aspirated four cylinder and continuously variable transmission (CVT) has a starting retail price of $19,510. The Corolla LE Eco, with government fuel economy ratings of 30/42 mpg, comes standard with a backup camera and is larger in size than the Fiesta. Another competitor, the 2014 Nissan Versa sedan, has a starting MSRP, including destination charge, of $14,800 for a Versa S Plus that is rated at 31/40 mpg. This model comes with 109-horsepower, four-cylinder engine and a CVT.

While the Fiesta’s three-cylinder engine is new to the United States, it has been used in Fords sold in Europe, where fuel prices are high.

Truth be told, Americans aren’t all that familiar with three-cylinder engines, and there are few cars sold in the United States that have them. One exception is the 2014 Mini Cooper Hardtop whose three-cylinder gasoline engine, like that in the Fiesta, is turbocharged.

Turbo boost helps three-cylinder engines provide a spunky performance and quicker acceleration than what would come from a naturally aspirated powerplant.

Three-cylinder engines also are inherently imbalanced, since two pistons go up and down at the same time vs. the singular remaining piston operating solo. In the Fiesta, Ford engineers installed special engine mounts to handle the engine vibrations and used the flywheel and front pulley to, in essence, cancel the imbalance. The effort worked so well that no passenger in the test Fiesta could tell that the car was propelled by a three cylinder. Everyone guessed it was a four cylinder.

To be sure, the Fiesta could sound and feel like it was working hard on long uphill stretches of highway and carried four adults and luggage.

But in most situations, the car, which weighed less than 2,700 pounds, was not anemic.

Zero to 60 miles per hour time is about 7 seconds, which is on par with typical sport utility vehicles, and the Fiesta was a comfortable, frugal traveler in city driving, on rural roads and on flat highways.

Torque peaks at 148 foot-pounds at 5,000 rpm, and the driver could work the five speed manual to get the most from the power band when needed.

Road noise and some wind noise came through into the passenger compartment. The ride was firm, not floaty, and passengers felt road bumps and pavement blemishes as mostly vibrations. This inexpensive car riding on 15-inch tires with steel wheels was agile, easy to maneuver and had better handling than expected.

The test Fiesta also had impeccable fit and finish, inside and out.

While the dashboard was dominated by plastic, the textures and gauges and controls were pleasant. Cloth seats up front gave good support and didn’t look bare-bones. But they had to be adjusted manually.

The back seat cushions were short, and legroom can feel tight at 31.2 inches. While there are three seats and seatbelts in the back seat, three people back there feels like too many.

But front-seat passenger and driver get good 42.2 inches of legroom, and trunk space of 12.8 cubic feet in the Fiesta sedan is generous for a subcompact.

The 2014 Fiesta sedan earned a four-out-of-five-stars rating, overall, from the federal government in crash tests.

But side crash test results were only good enough for two stars.

Consumer Reports magazine said predicted reliability for Fiesta cars is worse than average.

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